1. Field of the Invention
The present invention relates to a thin film magnetic head having a heater that is supplied with power and generates heat provided in the vicinity of an element.
2. Description of the Related Art
In general, a thin film magnetic head includes a reproducing element that reads out magnetic information from a recording medium using magnetoresistance and a recording element that is formed on the reproducing element and applies a recoding magnetic field to the recording medium to record magnetic information on the recording medium. As known in the art, the reproducing element is provided between a lower shield layer and an upper shield layer with gap layers interposed therebetween. For example, in a vertical recording type, the recording element includes a main magnetic pole layer and a return yoke layer that are exposed from a surface facing a recording medium, with a magnetic gap layer interposed therebetween, and a recording coil that applies a recoding magnetic field to the main magnetic pole layer. In recent years, the following structure has been proposed: a heater that is supplied with power and generates heat that is provided in the vicinity of an element; and the element protrudes toward a recording medium by thermal expansion such that the gap between the element and the recording medium is locally narrowed, thereby improving reproducing/recording performances.
In this thin film magnetic head, it is necessary to keep the surface of a metal material exposed from the surface facing a recording medium at the same potential in order to prevent the electrostatic damage of an element. Specifically, for example, the following structure has been proposed: a shunt line for applying the same reference potential is provided in each of an upper shield layer, a lower shield layer, and a return yoke layer. According to the structure including the shunt lines, when a reproducing element having a CPP structure in which a current flows in the vertical direction to the surface of a magnetoresistive film, such as a TMR element using tunneling magnetoresistance, is used, that is, when both the lower shield layer and the upper shield layer are not connected to the ground such that the lower shield layer and the upper shield layer serve as electrodes of the reproducing element, it is possible to prevent the electrostatic damage of the reproducing element. In addition, since it is not necessary to directly connect the lower shield layer, the upper shield layer, and the return yoke layer, noise generated from the return yoke layer has no adverse effect on the output of the reproducing element. JP-A-2004-206790 discloses a structure that applies a guide potential that is equal to that of the lower shield layer or the upper shield layer to a lower magnetic pole layer of a recording element.
However, in the thin film magnetic head having the heater provided in the vicinity of the element, when the shunt line is provided in the return yoke layer, heat generated from the heater is dissipated through the shunt line. As a result, the thermal efficiency of the heater (the ratio of the amount of heat transmitted to the element to the amount of heat generated by the heater) is lowered.